JPH10133055A - Photocoupler and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the reduction of coupling efficiency and to expand the allowance of the coupling efficiency on an incident position by specifying the taper shape of a 1st dielectric layer. SOLUTION: The photocoupler is constituted of a substrate 3, an optical wave guide 6 consisting of 1st and 2nd dielectric layers 1, 2 having parts of which film thickness is changed like a taper and a prism 4 stuck to the surface of the waveguide 6 by adhesives 5 and capable of making light incident upon the surface of the waveguide 6 at a prescribed angle. The taper shape of the 1st dielectric layer 1 is constituted so that a radiation pattern formed at the time of radiating light of wavelength λ from the optical waveguide part satisfies an inequality an-1 (1-rn )<an (1-rn+1 ) when a radiation coefficient in a section Xn-1 <X<Xn having a part of which film thickness is changed like a taper is αrn . In the inequality, rn =e×p (k0 αrn ΔX), k0 =2π/λand ΔX=Xn -Xn-1 .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical coupler used for optically coupling an optical waveguide device of an optical waveguide type optical pickup, for example, and a method of manufacturing the same.

[0002]

2. Description of the Related Art As a conventional optical coupler of this type, there is known an optical coupler provided with a prism as light introducing means and optically coupling incident light into an optical waveguide having no tapered structure by the prism.

In recent optical waveguide type optical pickups, it is required to further reduce the beam spot diameter in order to achieve more precise recording / reproducing. However,
In an optical coupler mounted on an optical waveguide type optical pickup,
There is a problem that the tolerance of the coupling efficiency with respect to the incident position becomes smaller as the incident beam diameter becomes smaller (the beam spot diameter becomes 30 μm or less). Therefore, it is necessary to solve this problem in order to cope with a recent tendency to further reduce the beam spot diameter.

[0004] To solve the above problem,
There is a prism coupler (hereinafter, referred to as a prism coupler) disclosed in Japanese Patent Application Laid-Open No. 4-289531. In this prism coupler, the coupling characteristic is changed by changing the propagation constant (a value having a real part indicating a phase constant and an imaginary part indicating an attenuation constant, a value determined by the thickness and refractive index of the optical waveguide) in the light propagation direction of the optical waveguide. Is adopted to improve the tolerance to the incident position. Specifically, as shown in FIG. 20, a method of tapering the second gab layer 104 is employed.

This prism coupler is a substrate (Si substrate)
After forming an SiO ₂ layer 107 on the substrate 101 and laminating the optical waveguide layer 102 and the first gap layer 103 thereon,
The second gap layer 104 laminated on the first gap layer 103 is tapered, and the tapered second gap layer 1 is formed.
The structure is such that a prism 106 is adhered to the substrate 04.

Here, the second gap layer 104 forms an edge (edge surface) 306 of the prism 304 when the prism is pressed against the surface of the optical waveguide to form a prism coupler.
(See FIG. 21), and the first gap layer 103 serves as an air gap to establish optical coupling.

FIG. 21 shows a prism coupler of a type in which a prism is crimped to an optical waveguide.
Is a first dielectric layer, 302 is a second dielectric layer, 303 is a substrate, 304 is a prism, 305 is an optical waveguide, and 306 is an edge of the prism.

Here, an optical coupler such as a prism coupler has the property of coupling with high efficiency to incident light that matches a radiation pattern when light exits the optical coupler. In a prism coupler, the second gap layer 1
The taper of 04 changes the radiation pattern to the desired shape. Specifically, the second gap layer 104 is tapered (forms a gentle taper of 1: 1000 or more),
The radiation pattern when light is extracted by this prism coupler is formed so as to radiate almost uniformly in the propagation direction of the optical waveguide with uniform intensity (in other words, regardless of the change in the incident position, the intensity of the radiation pattern is increased). It is utilized for the purpose of improving the coupling efficiency of an incident beam having a large beam diameter (by being transformed into a radiation pattern shape in which the radiation pattern becomes almost constant).

As another conventional example of this type of prism coupler, there is one disclosed in Japanese Patent Application Laid-Open No. 5-45532. FIG. 22 shows the structure of this prism coupler.
The optical waveguide layer (waveguide layer) is a tapered prism coupler.

[0010] Here, in the specification of Japanese Patent Application Laid-Open No. 5-45532, there is no description about the improvement of the coupling characteristics. However, even in the structure of FIG. An improvement in acceptability can be expected.

The prism coupler shown in FIG.
A prism 204 having a gap layer 205 laminated on a bottom surface (the surface on the side to be bonded to the optical waveguide) 206 is formed on an optical waveguide on which an optical waveguide layer 202 having a portion whose thickness changes in a tapered shape is formed on the optical waveguide 01. The waveguide layer 202 is bonded with an adhesive 203 having a refractive index substantially equal to that of the waveguide layer 202.

[0012]

As described above, FIG.
Has a structure in which a gently tapered portion is formed in the second gap layer 104 to intentionally change the radiation pattern. However, this prism coupler is used as an optical coupler for allowing a beam having a small beam diameter to enter. However, when the gradient of the tapered portion is changed), the distance between the edge 111 of the bonding portion and the edge 110 (the boundary between the tapered portion and the flat portion) of the tapered portion of the second gap layer 104 is determined by the coupling characteristic. Has some effect.

Here, since the prism coupler shown in FIG. 20 has no element for defining the linearity of the edge 111 of the bonding portion,
The distance between the tapered portion of the second gap layer 104 and the edge 110 cannot be accurately determined to optimize the coupling efficiency. Therefore, when the prism coupler of FIG. 20 is used as an optical coupler for incident a beam with a small beam diameter, it is necessary to minimize the decrease in coupling efficiency as much as possible and expand the tolerance of the coupling efficiency with respect to the incident position. There is a problem that it is difficult.

In addition, regarding the incident position for obtaining the optimum coupling efficiency with respect to the incident beam, the edge 1 of the bonding portion is also required.
There is also a problem that it is difficult to determine an optimal incident position of the incident beam with respect to the optical waveguide since linearity is not ensured at an intersection line between the optical waveguide 11 and the optical waveguide surface.

Further, in order to taper the second gap layer, it is necessary to increase the thickness of the waveguide element in order to obtain a desired radiation pattern from the prism coupler. For this reason,
Since the degree of freedom in element design is reduced and the film stress is increased, there is also a problem that it is difficult to manufacture with high accuracy.

On the other hand, in the prism coupler shown in FIG. 22, the tolerance of the coupling characteristic with respect to the incident position cannot be expanded even if the optical waveguide layer 202 is simply tapered. The reason will be described below.

First, it is premised that the coupling efficiency of the optical coupler is determined by the radiation characteristics when the optical coupler functions to emit light (light when the optical coupler is used for extracting light from the optical waveguide). High efficiency when the incident light having a closer phase and intensity distribution enters the radiation pattern).

When the optical waveguide layer 202 is tapered, as shown in FIG. 23, the radiation pattern becomes one of a monotonically decreasing type and a deformation type depending on the structure of the tapered portion of the optical coupler. Here, the monotonically decreasing radiation pattern is a radiation pattern obtained even when the optical waveguide layer is not tapered, and the coupling efficiency changes with respect to a change in the incident position in the traveling direction of light after coupling to the optical waveguide. The shape is easy, and the tolerance to the incident position is smaller than that of the modified radiation pattern. Therefore, in order to increase the tolerance of the coupling characteristic with respect to the incident position, it is better that the radiation pattern of the optical coupler is shaped so that its intensity becomes almost uniform with respect to the change of the incident position. It is necessary to have a modified radiation pattern consisting of a curve having a maximum point in the middle and having a gentle downward slope on both sides.

However, in the prism coupler of FIG.
Since the structure of the tapered portion is not specified in consideration of this point, there is a problem that the tolerance of the coupling efficiency with respect to the incident position cannot be expanded for the above-described reason.

In addition, the prism coupler shown in FIG. 22 has a structure in which a bism 204 in which a gap layer 205 is laminated on the back surface 206 is bonded to the optical waveguide with an adhesive 203 having the same refractive index as the optical waveguide layer 202. The positioning error when the 204 is adhered to the optical waveguide becomes the amount of displacement from the optimal positional relationship (maximizing the coupling efficiency) between the edge 208 of the prism 204 and the edge 207 of the tapered portion of the optical waveguide layer 202 as it is.

Further, in the optical coupler shown in FIG.
3 is not guaranteed, it is difficult to optimize the distance between the edge 208 of the prism 204 and the edge 207 of the tapered portion of the optical waveguide layer 202, and the film thickness is controlled on the optical waveguide layer 202. Since the adhesive layer 203, which is difficult to achieve, is sandwiched, it is very difficult to accurately set the distance between the edges.

For the reasons described above, in the prism coupler of FIG. 22, it is difficult to reduce the coupling efficiency as much as possible and to expand the tolerance of the coupling efficiency with respect to the incident position.

As described above, in the conventional prism coupler,
Since it was difficult to reduce the coupling efficiency as much as possible and expand the tolerance of the coupling efficiency with respect to the incident position, it is required to further reduce the beam spot diameter in order to achieve more precise recording / reproduction. There is a problem that can not cope with recent technological trends.

The present invention has been made in view of such circumstances, and it is possible to minimize the decrease in the coupling efficiency of the incident light to the optical coupler and to increase the tolerance of the coupling efficiency with respect to the incident position. It is an object of the present invention to provide an optical coupler that can cope with recent technical trends that require a smaller beam spot diameter in order to achieve more precise recording / reproduction, and a method of manufacturing the same.

[0025]

An optical coupler according to the present invention comprises a substrate and a portion laminated on the substrate and having a portion in which a film thickness changes in a tapered shape in an X-axis direction in which incident light proceeds after coupling. An optical waveguide comprising a first dielectric layer and a second dielectric layer laminated on the first dielectric layer, and light is introduced by light introducing means adhered on the optical waveguide via an adhesive portion; An optical coupler that is incident on the surface of the optical waveguide at a predetermined angle,
In the bonding portion, the line of intersection with the surface of the optical waveguide becomes a straight line,
In addition, an edge surface having a portion not in contact with either the light introducing means or the surface of the optical waveguide is formed, and a section X _{n-1 having} a portion where the film thickness of the first dielectric layer changes to a tapered shape.
<The emission coefficient at X <X _n and alpha _rn, when the distance from the edge surface of the adhesive portion is the amplitude at the position of X _n and a _n,
As radiation pattern when radiated from the optical waveguide the light of the wavelength λ by using the optical coupler, which satisfies the following conditions _{(1), a n-1 (1-} r n) <a n _{(1-r n + 1)} ... (1) _{However, r n = exp (k 0} α rn △ X) k 0 = 2π / λ △ X = X n -X n-1 taper of the first dielectric layer The shape is set, thereby achieving the above object.

Preferably, the taper length t of the taper shape, the thickness s of the second dielectric layer, the maximum thickness D and the minimum thickness d of the first dielectric layer satisfy the following conditions. 5 [μm] <t <15 [μm], 300 [nm] <s <
400 [nm], 540 [nm] <D <600 [n
m], 320 [nm] <d <400 [nm] The tapered shape is set.

Preferably, the height h of the edge surface of the bonding portion from the surface of the optical waveguide is such that the Airy radius of the incident beam spot is r _A, and the incident angle on the surface of the optical waveguide is θ _1. When h is set, h> 2r _A / sin θ ₁ ′ (2) is set so as to satisfy the condition of the following equation (2).

[0028] Preferably, a prism is used as the light introducing means.

Preferably, a dielectric plate is used as the light introducing means.

Preferably, an antireflection coating is applied to the surface of the dielectric plate.

Further, the method for manufacturing an optical coupler according to the present invention is the method for manufacturing an optical coupler according to any one of the above, wherein a step of applying a photoresist to the surface of the optical waveguide; A step of forming a groove for injecting an adhesive, a step of adjusting the position of the light introducing means on the surface of the optical waveguide, and a step of bonding and fixing the light introducing means to the surface of the optical waveguide. And the step of removing the photoresist, thereby achieving the above object.

Further, the method for manufacturing an optical coupler according to the present invention is a method for manufacturing an optical coupler, wherein the light introducing means is a prism, wherein a step of applying a photoresist to the surface of the optical waveguide, Forming a groove for injecting an adhesive on a resist, arranging the prism on the surface of the optical waveguide by adjusting the position so as to straddle the groove, and placing the light introducing means on the surface of the optical waveguide. The method includes a step of bonding and fixing, and a step of removing the photoresist, whereby the object is achieved.

Preferably, in the above manufacturing method, w> h, where h is the height of the edge surface of the bonding portion from the surface of the optical waveguide so that the thickness w of the photoresist satisfies the following condition. Set.

Preferably, the post-process of forming a groove on the photoresist includes a process of performing RIE on the surface of the optical waveguide.

Preferably, the step of adhering and fixing the light introducing means to the surface of the optical waveguide is performed using a photocurable adhesive.

It should be noted that the tapered shape referred to in the present invention means the first shape.
The concept includes not only a shape in which the minimum and maximum portions of the thickness of the dielectric layer are connected by a straight line, but also a shape in which the film thickness changes gradually and continuously.

The operation of the present invention will be described below with reference to FIGS.

FIG. 1 shows the structure of a prism coupler according to Embodiment 1 of the present invention. The prism coupler is laminated on a substrate 3 and has a tapered (tapered) film thickness. An optical waveguide 6 composed of a first dielectric layer 1 having a changing portion and a second dielectric layer 2 laminated on the first dielectric layer 1, and an adhesive (adhesive portion) on the surface thereof
And a prism 4 for adhering light to the surface of the optical waveguide 6 at a predetermined angle.

Here, the tapered shape of the first dielectric layer 1 is
The shape is set to satisfy the relationship of the above equation (1).
FIG. 2 shows r _n in the above equation (1). Where r _n
When the optical coupler (prism coupler) functions to emit light, the amplitude attenuation rate of the light during the propagation distance ΔX, that is, the propagating light during the propagation between the sections X _{n-1 to} X _n Represents the rate of attenuation of the electric field strength of FIG.

When the tapered shape is determined so as to satisfy the expression (1), the radiation pattern becomes a deformation type shown in FIG. 23 for the reason described later.

Here, the radiation coefficient α _rn is given by the following (3a)
It can be obtained as the imaginary part of the solution (having a complex number solution) β _TE and β _TM of equation (3) consisting of equations (3) to (3d).

[0042]

(Equation 1)

However, the above equation (3) shows that the first dielectric layer 301 having a film thickness q and a refractive index n ₁ , a thickness s and a refractive index n ₂ are formed on a substrate 303 having a refractive index n _s as shown in FIG. Second dielectric layer 302
And an optical waveguide 305 formed by laminating a equation holds in the case where the prism coupler is pressed against a prism 304 having a refractive index n _b, a first dielectric layer 1 of the taper portion 8 of the prism coupler of FIG 1 interval ( x _n-1 <emission coefficient alpha _rn at x <x _n) is the thickness of the average in the same section as d _n,
In FIG. 21, when there is no gap and the prism 304 is replaced with the bonding portion 5 (h = 0), the equation (3) is used.
It can be obtained as a solution when the q = d _n in. Hereafter, n _b is used as a symbol indicating the refractive index of the bonding portion 5.

The coupling efficiency of the optical coupler depends on how much the radiation pattern of the optical coupler matches the profile of the incident beam (assuming a Gaussian amplitude distribution).
The phase constant of the incident light and the phase constant specific to the optical coupler (Equation (3)
23. More specifically, the phase component exp is added to the radiation pattern of the optical coupler shown in FIG.
It can be obtained almost correctly by an overlap integral of a function multiplied by {−jB (x) x} and a function f _i (x) that gives the amplitude distribution of the incident beam.

Where B (x) is β _TE or β in the x-axis direction.
_This is a function representing the change of the real part of _TM , and the function f _i (x) is expressed by the following equation (4).

[0046] _{f i (x) = exp (} -jk 0 n b sinθ i 'x-4x 2 / L 2) ... (4) where, theta _i': incident angle W _e of the optical waveguide surface: light intensity 1 / E ² , the incident beam diameter L = W _e / cos θ _i ′.

Therefore, if the radiation pattern of the optical coupler is a modified radiation pattern shown in FIG. 23 which is substantially uniform in the light traveling direction in the optical waveguide 6, the coupling efficiency to the optical waveguide 6 can be reduced. The tolerance for the incident position can be expanded.

Here, in the optical coupler to which the present invention is applied, the adhesive constituting the adhesive portion, the substrate, and the materials of the first dielectric layer and the second dielectric layer are each a refractive index of 1.56.
1.58, refractive index 1.44 to 1.46, refractive index 1.5
Since a material having a refractive index of 2 to 1.56 and a refractive index of 1.42 to 1.44 is frequently used, the taper length t of the taper shape, the thickness s of the second dielectric layer, and the maximum thickness D of the first dielectric layer are set. And 5 [μm] <t <15 [μm] and 300 [nm] <s <so that the minimum film thickness d satisfies the following condition.
400 [nm], 540 [nm] <D <600 [n
m], 320 [nm] <d <400 [nm] When the tapered shape is set, an optical coupler having the above-described operation can be realized.

Also, an edge surface 7 is formed on the bonding portion 5 so that the line of intersection with the surface of the optical waveguide 6 is straight, and the light introducing means and the edge surface 7 having a portion not in contact with any of the surfaces of the optical waveguide 6. According to this, the distance between the edge of the tapered portion of the first dielectric layer 1 and the intersection line between the edge surface 7 of the bonding portion and the surface of the optical waveguide 6 can be accurately determined. Therefore, the deviation dx of the distance between the edge of the tapered portion of the first dielectric layer 1 and the edge surface 7 of the bonding portion from the optimal value can be easily eliminated, and as shown in FIG. Reduction can be minimized.

It should be noted that the coupling characteristics shown in FIG.
This was obtained under the test conditions shown in (b).

Further, a prism is used as the light introducing means,
When the height h of the edge surface of the bonding portion from the surface of the optical waveguide is set so as to satisfy the above expression (2), the bonding portion is formed into a thin film by the multiple reflection light generated by the reflection at the interface between the bonding agent and the bottom surface of the prism. And completely eliminates the possibility that the coupling efficiency becomes unstable. The details will be described later.

Further, according to the configuration using the dielectric plate as the light introducing means, the production cost can be reduced because the dielectric plate is easier to manufacture than the prism.

Further, in this case, according to the configuration in which the antireflection coating is applied to the dielectric surface, there is an advantage that the reflected light can be reduced.

Further, according to the manufacturing method of the present invention, the position of the line of intersection of the edge of the adhesive with the surface of the optical waveguide is adjusted with respect to the edge of the tapered portion of the first dielectric layer by photolithography. Therefore, the distance between the line of intersection of the edge of the bonding portion with the optical waveguide surface and the edge of the tapered portion of the first dielectric layer can be determined with high accuracy. In addition, since the linearity of the line of intersection between the edge surface of the bonding portion and the surface of the optical waveguide can be realized by the photomask, highly accurate linearity can be realized.

Further, according to the configuration in which the prism is disposed on the photoresist so as to straddle the groove formed by the photoresist, the prism contacts the photoresist surface at two places, so that the optical waveguide surface and the prism bottom surface are connected to each other. Parallelism can be improved. As a result, when the light is incident at the optimum incident angle (the incident angle at which the coupling efficiency to the optical coupler is the maximum), the base angle φ of the prism determined to minimize the reflection at the incident surface, and the optical waveguide surface Deviation from the angle formed by the incident angle to the light can be reduced. For this reason, it is possible to suppress a decrease in coupling efficiency due to a shift of the incident angle to the optical coupler from the optimum incident angle.

The thickness w of the photoresist and the height h of the edge surface of the bonding portion from the surface of the optical waveguide are w> h.
By setting so as to prevent the bonding portion from functioning as a thin film.

According to the structure in which RIE processing (oxygen plasma processing) is performed as a post-processing for forming a groove on the photoresist, the organic residue of the developing solution of the photoresist and the deterioration formed on the surface of the optical waveguide are formed. Since the layer can be removed, the adhesive strength to the optical waveguide can be increased.

Further, by using a photocurable adhesive as the adhesive, the curing time can be shortened, and the change in the adjustment position during the curing process can be minimized.

[0059]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below with reference to the drawings.

(Embodiment 1) FIGS. 1 to 3 show Embodiment 1 of the optical coupler of the present invention.

<Structure of Optical Coupler of First Embodiment> The optical coupler of the first embodiment has a first dielectric layer 1 and a second dielectric layer 2 on a substrate 3 as shown in FIG. Are laminated in this order with a predetermined thickness, thereby forming an optical waveguide 6, and a basic structure in which a prism 4 is bonded to the surface of the optical waveguide 6 via a bonding portion (adhesive) 5. That is, the optical coupler of the first embodiment is a prism coupler.

The first dielectric layer 1 has a portion where the film thickness changes in a tapered shape (hereinafter referred to as a tapered portion 8). Further, a rear end surface corresponding to the right side in the drawing of the bonding portion 5 is an edge surface 7 for optical coupling. The specific shape of the tapered portion 8 will be described later.

Here, the conditions for forming the optical coupler are as follows:
The refractive index of the first dielectric layer 1 is n ₁ , the refractive index of the second dielectric layer is n ₂ , the refractive index of the substrate 3 is n _s , and the refractive index of the prism 4 is n.
when _p and the refractive index of the adhesive 5 and n _b, respectively the refractive index of the need to meet the _{n 1> n 2, n 1} > n s, the relationship of n _b> n _1. Further, it is preferable that the adhesive used as the bonding portion 5 is transparent.

In this optical coupler, the prism 4 is bonded to the optical waveguide 6, but the prism 4 only plays a role of guiding light from the air to a higher refractive index region than the waveguide layer. It is. That is, what actually relates to optical coupling is the edge surface 7 of the bonding portion 5, and the principle of optical coupling is as follows.

<Principle of Light Coupling> The incident light that reaches the vicinity of the edge surface 7 of the bonding portion 5 through the prism 4 is incident on the boundary between the bonding portion 5 and the second dielectric layer 2 at an incident angle of total reflection. Nevertheless, the light passes through the second dielectric layer 2 in a tunnel effect and enters the first dielectric layer 1. However, the light is not totally transmitted to the substrate 3 side but is totally reflected, and goes to the surface direction of the optical waveguide 6.
This time, since there is no adhesive portion in contact with the second dielectric layer 2 above the waveguide layer (the first dielectric layer 1), it is totally reflected there again,
Thereafter, the light propagates by repeating total reflection.

<Constituent Materials of Optical Coupler of First Embodiment> The constituent materials of the optical coupler of FIG. 1 will be described below. The substrate 3 changes according to the use of the optical waveguide element forming the optical coupler, and is not limited to a simple dielectric substrate such as a glass substrate, but also an Si substrate as used as an optical coupler of an optical waveguide element integrated with a light receiving element. A substrate on which a dielectric layer (PSG [phosphorus-doped silicate glass], SiO ₂ , SOG [glass material capable of spin coating], etc.) is formed is used.

The first dielectric layer 1 is changed depending on the waveguide layer of the optical waveguide element forming the optical coupler, and is made of SiON known as a material of the waveguide layer of the optical waveguide element or a product name of Corning Corporation. # 7059 glass or the like can be a material.
In the first embodiment and the following embodiments, the first dielectric layer 1
As the material for the glass, Corning's trade name # 7059 glass is used.

The refractive index n ₂ of the second dielectric layer must be lower than the refractive index n _{1 of} the first dielectric layer 1. 70
When 59 glass is used, the material of the second dielectric layer 2 includes:
SiO ₂ , SOG, etc., having a lower refraction rate than this, are used.

The contents of FIGS. 2 and 3 have been described in connection with the above operation, and therefore will not be described here.

(Embodiment 2) FIG. 4 shows Embodiment 2 of the optical coupler of the present invention. The optical coupler according to the second embodiment includes a substrate 13
As in the case of forming a photodiode,
The refractive index n _s = 1.4 as the dielectric layer 21 on the substrate 20
A substrate on which an SiO ₂ layer of No. 4 was formed was used. In the second embodiment, the first dielectric layer 11 has a refractive index n ₁ = 1.53.
The second dielectric layer 12 is made of SiO ₂ (n ₂ = n ₂₎ whose refractive index n ₂ is smaller than n ₁ , n _p and n _b.
1.43). These constitute the optical waveguide 16. However, the values of the refractive index and the values of the refractive index shown below are based on the measured values when the wavelength of the incident light is 780 [nm].

<Method of Setting Refractive Index of Prism and Refractive Index of Adhesive> A method of setting the refractive index of the prism and the refractive index of the adhesive will be described below, taking the optical coupler of the second embodiment as an example.

Regarding the refractive index n _p of the prism 14,
n ₁ , n ₂ , and n _s , and the prism 1
4 and for suppressing the reflection at the interface between the adhesive portion 15, or the same as the refractive index n _b of the adhesive, more preferably close to this. For example, as shown in FIG. 4, θ _bi is an incident angle at the interface between the prism 14 and the bonding portion 15, and the reflectance at the interface between the prism 14 and the bonding portion 15 is suppressed to a desired value R or less. In this case, the refractive index n _b of the adhesive 5 is set to the following (5)
It is necessary to determine so as to satisfy Expression (6) and Expression (6).

[N _p cos θ _bi − (n _b ² −n _p ² sin ² θ _bi ) ^1/2 ] ² / [n _p cos θ _bi − (n _b ² −n _p ² sin ² θ _bi ) ^1/2 ] ² > R (5) [n _b cos θ _bi − (n _p / n _b ) · (n _b ² −n _p ² sin ² θ _bi ) ^1/2 ] ² / [n _b cos θ _bi − (n _p / N _b ) · (n _b ² −n _p ² sin ² θ _bi ) ^1/2 ] ² > R (6) Therefore, a prism having a refractive index n _p of 1.57 (for example, glass material LF5 (manufactured by Ohara Optical Glass Co., Ltd.) Product name),
In order to make the reflection at the interface between the prism 14 and the bonding portion 15 almost zero, an adhesive whose refractive index n _b is close to the refractive index n _p (= 1.57) of the prism is used as the adhesive 5. For example, Loctite UV curable adhesive LX-2310
C and the like apply to this condition.

<Shape of Edge Surface of Adhesive Portion> The edge surface 17 of the adhesive portion 15 is formed such that the line of intersection with the optical waveguide 16 is straight. This satisfies the condition for accurately determining the position where the edge surface 17 of the bonding portion 15 is formed with respect to the edge 19 of the tapered portion 18 of the first dielectric layer 11 of the optical waveguide 16. This is because the distance between the optical waveguide 16 and the edge 19 of the tapered portion 18 of the first dielectric layer 11 in the optical waveguide 16 can be determined so as to maximize the coupling efficiency.

<Taper Shape of Tapered Portion> As shown in FIG. 4, the tapered shape of the tapered portion 18 according to the second embodiment is a linear shape having a length t and a thickness varying from d to D (D> d). Is a tapered portion. The position of the edge 19 of the tapered portion 18 and the position of the edge surface 17 of the bonding portion 5 do not necessarily have to match, but in the second embodiment, the edge 19 of the tapered portion 18 of the optical coupler is maximized so that the coupling efficiency is maximized. Position and bonding part 15
Of the edge surfaces 17 of the two.

The conditions necessary to expand the tolerance of the coupling efficiency of the incident light to the optical coupler with respect to the incident position (represented by the distance from the edge surface 17 of the bonding portion 15 to the prism 14) are as described above. FIG. 23 shows the radiation characteristics of the prism coupler.
It is necessary to be not the monotonically decreasing type but the modified type shown in FIG.

For this purpose, the direction in which the incident light travels after the coupling is defined as the x-axis, and a section (x _n-1 <x <) where the film thickness of the first dielectric layer 11 changes in a tapered shape. _xn )
The radiation coefficient is alpha _rn at a distance from the edge surface 17 of the adhesive portion 15 when the amplitude at the position of x _n and a _n, emits from the optical waveguide to light of wavelength λ by using the optical coupler In this case, it is necessary that the radiation pattern satisfies the relationship of the above equation (1).

Here, the values of the refractive index and the film thickness of each part constituting the optical coupler of the second embodiment, n _b = 1.57, n _a =
1.0, n ₂ = 1.43, n ₁ = 1.53, n _s = 1.4
4, h by applying (see FIG. 9) = 0, q = d n to each of the above (3) to calculate the radiation pattern calculated radiation coefficient alpha _rn. In the optical coupler of the second embodiment, SiO ₂
The thickness (expressed as s) of the cladding layer (second dielectric layer) 12 is 350 [nm], and the thickness of the tapered portion 18 of the # 7059 waveguide layer 11 is d = 320 [nm]. From D to 570 [nm], and the taper length t is 10
[Μm] (hereinafter referred to as an optical coupler structure 50).
1). Here, when the taper length t is 10 [μm], a radiation pattern as shown in FIG. 5A that satisfies the relationship of the expression (1) is obtained. However, the taper length t is 20 μ
m] or 30 [μm], FIG.
The radiation pattern shown in FIG.

Further, as the taper length t is longer, the incident position of the coupling efficiency (from the edge surface 17 of the bonding portion 15 to the prism 14)
6 (a), the slope of the curve of the radiation pattern becomes gentler. In FIG. 6 (a), the change in the coupling efficiency with respect to the incident position is the largest when the taper length is 30 [μm]. Coming down. However, since a decrease in the maximum value of the coupling efficiency also occurs due to this dulling, it is desirable to prevent this.

For example, if the incident beam spot diameter L is 30
When the suppression of the decrease in the coupling efficiency is taken into consideration when [μm] is considered, the tolerance of the coupling efficiency for the incident position of the optical coupler structure defined in the optical coupler structure 501 minimizes the decrease in the coupling efficiency. Expanded above. Figure 24 below
(A) and (b) show the results of comparison with the conventional example.

Tolerance to the incident position of the optical coupler structure 501 according to the second embodiment (defined as coupling efficiency of 60% or more)
The radiation characteristics of the optical coupler shown in FIG. 24 in which the structure is optimized so that the coupling efficiency is maximized with respect to the incident beam spot diameter L = 30 [μm] without tapering the # 7059 waveguide layer 11 (see FIG. 24 (b)), the tolerance from the optimum incident position where the coupling efficiency is maximized is ± 7.5 [μ].
m] (see FIG. 24 (b)) to ± 9 [μm] (see FIG.
(See (a)).

[0082] Further, as shown in FIG. 5 (b), SiO ₂
The thickness s of the cladding layer 12 is 350 [nm], and # 7
Since the thickness of the 059 waveguide layer 11 is d = 400 [nm] and D =
570 [nm] and the taper length t is 10 [μm]
Even with a structure of an optical coupler having a taper of 20 [μm] or 30 [μm], a radiation pattern similar to that shown in FIG. 5A can be obtained, and as shown in FIG. Tolerance is expanded.

Here, in the structure of the optical coupler, when the taper length t is 10 [μm] (hereinafter the optical coupler structure 50)
2), it is possible to increase the tolerance of the coupling efficiency with respect to the incident position while minimizing the decrease in the coupling efficiency. Specifically, the incident beam spot diameter L is set to 30 [μ
m], the optimum incidence position is compared with the radiation pattern of the optical coupler shown in FIG. 24 (see FIG. 24 (b)) in terms of the tolerance to the incidence position (defined by the coupling efficiency of 60% or more). Is ± 7.5 [μm] (FIG. 24 (b)
) To ± 9 [μm] (see FIG. 6B).

<Prism Shape> With respect to the shape of the prism, in the case of a trapezoidal prism as shown in FIG. 4, the base angle φ of the prism 14 is made substantially equal to θ _op expressed by the following equation (7). The slopes of the prisms are almost perpendicular to the optimal incident directions of the TE mode polarized light and the TM mode polarized light, respectively, so that the coupling efficiency between the TE mode polarized light and the TM mode polarized light is almost equal and approaches the maximum.

Θ _op = (θ _TE + θ _TM ) / 2 (7) In the equation (7), θ _TE and θ _TM are TE mode polarized light and T
Optical waveguide 1 when coupling efficiency of M-mode polarized light is maximized
6 represents the incident angle θ _i ′ on the surface. Since these θ _TE and θ _TM are values determined from the incident angle characteristic (see FIG. 7) of the coupling efficiency that changes depending on the taper shape, the base angle φ of the prism also corresponds to the change in the taper structure. Change. For the optical coupler structure 501, FIG.
From θ _TE = 68.4 ° and θ _TM = 68.0 °,
The base angle φ of the prism is 68.2 ° (= θ _op ).

Therefore, for the optical coupler structure 501,
By setting the incident angle θ _i to the optical coupler to 68.2 °, the best coupling characteristics can be obtained. On the other hand, also for the optical coupler structure 502, FIG. 7 shows that θ _TE = 69.3.
°, θ _TM = 68.9 °, the base angle φ of the prism is 69.1 °, and the incident angle θ _i to the optical coupler is 6
By setting the angle to 9.1 °, the best coupling characteristics can be obtained.

Here, the shape of the prism may be determined so as to minimize the loss due to reflection in the light incident direction, and may be changed in accordance with the tapered shape. in addition,
In addition to the shapes shown in FIGS. 1 and 4, it is also possible to use a prism 22 having a shape that is totally reflected and made incident as shown in FIG.

In FIG. 8, portions other than the prism 22 are denoted by the same reference numerals as those in FIG.

<How to determine the height h of the edge surface of the bonding portion> Next, the edge surface 17 formed on the bonding portion 15 will be described with reference to FIG.
How to determine the height h from the surface of the optical waveguide 16 will be described. In the optical coupler of the second embodiment, the prism 14 or the adhesive 15
Are protruding by a length P _L from the position of the intersection between the edge surface 17 of the bonding portion 15 and the surface of the optical waveguide 16 (see FIGS. 1 and 9; FIG. This shows a case where the agent 15 adheres to the side of the prism 14 facing the optical waveguide 16) If the height h from the surface of the optical waveguide 16 is not sufficient, a part of the bonding portion 15 or a high refractive index region such as the prism 14 The light coupled to the optical waveguide 16, that is, the guided light is transmitted toward the (dielectric region having a higher refractive index than the second dielectric layer 12 and the first dielectric layer 11) as shown in FIG. ), The coupling efficiency decreases.

Therefore, in order to eliminate the influence of recombination, the length of the protruding part of the prism 14 or the bonding portion 15 is set to P _L and the film thickness of the first dielectric layer 11 is set to the maximum value D.
TE, TM solutions beta _TE equations represented by equation (3) for each polarization, a function of the the larger absolute value alpha _rD (h among the emission coefficient is the imaginary part of the beta _TM when it becomes ), The optical waveguide surface 1 on the edge surface 17 of the bonding portion 15
It is preferable that the height h from 6 satisfies the condition of the following expression (8).

1-exp (k ₀ α _rD P _L ) ≒ 1 (8) If the condition of the above equation (8) is satisfied, it is possible to secure an edge surface height that can prevent a decrease in coupling efficiency due to recombination. However, even when the prism 14 or a part of the adhesive portion 15 does not protrude, the refractive index of the adhesive 15 changes depending on the ambient temperature and various conditions.
6 so that the bonding portion 15 between the first and sixth does not function as a thin film.
It is more preferable to determine the height of the edge surface 17 of the bonding portion 15. Here, the condition that the bonding portion 15 between the prism 14 and the optical waveguide 16 does not function as a thin film is that the height h is determined so as to suppress multiple reflection, and the radius r _A of the airy disk of the incident beam spot is set. Based on
By removing multiple reflections in the air disk, the prism 1
It is considered that the possibility that the bonding portion 15 between the optical waveguide 4 and the optical waveguide 16 functions as a thin film can be almost completely eliminated. Therefore, the height h of the edge surface is preferably determined so as to satisfy the condition of the following expression (2).

H> 2r _A / sin θ _i ′ (2) For example, for the optical coupler structure 501 of the present embodiment,
When the incident beam spot diameter L is 30 [μm], the NA of the condenser lens can be calculated as approximately 0.057.
r _A is calculated from r _A = 0.61λ (= 780 nm) / NA.
4 [μm], and FIG. 7 shows that θ _i ′ is 68.2 ° (= θ
_op ), the height h of the edge surface 17 of the bonding portion 15
Is 18 [μm] or more from the condition of the above equation (2).

<Method of Manufacturing Optical Coupler of Second Embodiment> Next, taking the case of forming the optical coupler structure 501 as an example,
FIGS. 10A to 10C show a manufacturing process of an optical coupler using a groove formed in a photoresist in order to form an edge surface 17.
Explanation will be given according to (g).

First, as shown in FIG.
A photoresist 51 is applied on an optical waveguide 16 formed by laminating a first dielectric layer 11 and a second dielectric layer 12 on 3.

Here, the thickness w of the photoresist 51 corresponds to the height of the edge surface 17, and the refractive index of the adhesive 15 changes depending on the ambient temperature and various conditions. The thickness w of the photoresist is determined so as to satisfy the condition of the above-mentioned formula (2) so that the bonding portion 15 therebetween does not function as a thin film, and the lower limit value 18 [μ] satisfying the relationship of w> h
m] or more.

Although FIG. 10 shows that the photoresist 51 is applied so as not to conform to the shape of the tapered portion 18 of the optical waveguide 16, the thickness of the photoresist 51 is larger than the thickness of the photoresist 51. 18 is small, the surface of the photoresist 51 after application is
It means that it is almost parallel to the surface.

Next, as shown in FIGS. 7B and 7C, a groove 52 for injecting an adhesive is formed in the photoresist 51 by patterning. After the formation of the groove 52, the surface of the optical waveguide 16 is subjected to RIE treatment (oxygen plasma treatment) to remove organic residues of the developing solution of the photoresist 51 and the altered layer formed on the surface of the optical waveguide 16. can do.

Next, as shown in FIGS. 9D and 9E, the edge B of the prism 14 is
Position adjusting device 5 so as to be parallel to edge C of the upper groove.
Adjust the position using 3. After the adjustment, the prism 14 is pressed onto the photoresist 51 applied to the optical waveguide 16 while being held at the adjusted position by the position adjusting device 53. Here, when the prism 14 is placed on the photoresist 51 so as to straddle the groove 52 formed by the photoresist 51, the prism 14 comes into contact with the surface of the photoresist 51 at two places. Parallelism is improved. As a result, the base angle φ of the prism 14 determined so as to minimize the reflection on the incident surface when the light is incident at the optimum incident angle (the incident angle at which the coupling efficiency to the optical coupler is maximized).
And the angle between the angle of incidence and the angle of incidence on the surface of the optical waveguide 16 can be suppressed to a small value. For this reason, it is possible to suppress a decrease in coupling efficiency due to a shift of the incident angle to the optical coupler from the optimum incident angle.

Next, as shown in FIG. 9F, a photo-curable adhesive 15 such as UV-curable is injected into the adhesive injection groove 52, and bonded by light irradiation (UV light irradiation). The agent 15 is solidified (cured) to fix the prism 14. Here, the adhesive 15 to be used may be other than the photo-curable one. However, if the photo-curable adhesive 15 is used, the time required for fixing is short, and the bonding due to the displacement of the prism until the fixing is performed. There is an advantage that reduction in efficiency can be reduced.

As for the selection of the adhesive 15 and the photoresist 51, a combination chemically stable when they come into contact with each other is selected. For example, the adhesive 15 may have Loctite product name L
In the case of using X-2310C, a photoresist (trade name: positive photoresist PMER) manufactured by Tokyo Ohkasha may be selected as the photoresist 51.

Next, as shown in FIG. 9G, after the prism 14 is fixed by bonding, the photoresist 51 is removed.

The removal of the portion of the photoresist 51 sandwiched between the adhesive 15 and the optical waveguide 16 is performed by removing the adhesive 1
The larger the distance between the optical waveguide 5 and the optical waveguide 16, the faster the process proceeds. Therefore, it is more preferable to apply the photoresist 51 thickly so that the photoresist 51 in the portion sandwiched between the adhesive 15 and the optical waveguide 16 is easily removed. . In the present embodiment, thick coating is performed using a highly viscous photoresist 51. More specifically, the positive photoresist PMER is applied in a superimposed manner (after the first application, baked and applied repeatedly), and the total thickness w of the photoresist 51 is 30 [μm]. As a result, the height h of the edge surface 17 of the bonding portion 15 of the manufactured optical coupler is 30 [μm].

Through the above manufacturing steps, the photoresist 5
An edge surface 17 corresponding to the edge B of the prism 14 is formed on the bonding portion 15 in a form in which the groove shape of 1 is copied.

By using this manufacturing method, the bonding portion 15
The linearity of the line of intersection of the edge surface 17 with the surface of the optical waveguide 16 is secured with an accuracy corresponding to the linearity of the photomask, and in the optical coupler of FIG. Tapered portion 18 of body layer (# 7059 waveguide layer) 11
Can be positioned with high accuracy.

Note that the edge surface of the photoresist 51 is not limited to 90 ° with respect to the surface of the optical waveguide 16 and may be formed at an angle smaller than 90 ° with respect to the surface of the optical waveguide 16 as shown in FIG. Good. For example, when the edge surface of the photoresist 51 forms an angle of 70 ° with the surface of the optical waveguide 16, the edge surface 17 of the bonding portion 15 of the optical coupler is formed.
Also form an angle of 70 ° with the surface of the optical waveguide 16.

However, the inclination of the edge surface 17 with respect to the surface of the optical waveguide 16 does not cause a serious problem that lowers the coupling efficiency of the optical coupler. Also, the prism 1 at the time of fabrication
4 cannot be completely adhered to the photoresist 51, the adhesive state is such that a part of the adhesive 15 is excessively adhered to the surface of the prism 14 facing the optical waveguide 16 as shown in FIG. It does not reduce efficiency.

(Embodiment 3) FIG. 12 shows Embodiment 3 of the optical coupler of the present invention. In the optical coupler according to the third embodiment, the dielectric plate 34 is used instead of the prism as the light introducing means. Since the dielectric plate 34 is easier to process than a prism, there is an advantage that the manufacturing cost of the optical coupler can be reduced.

Here, the principle of incidence of the optical coupler is the same as that of the second embodiment, and the light that has entered the dielectric plate 34 and passed through the bonding portion 35 The optical waveguide 36 is coupled to the optical waveguide 36. Therefore, even when the dielectric plate 34 is used, if the edge surface 37 having a predetermined height h from the surface of the optical waveguide 36 is formed on the bonding portion 35,
The same function as the optical coupler of FIG. 4 can be performed. Therefore, also in the optical coupler of the third embodiment, the tolerance of the coupling efficiency with respect to the incident position can be expanded by determining the tapered structure of the optical coupler so that the radiation pattern satisfies the condition of the expression (1).

Specifically, the refractive index n _s on the Si substrate 40
# 7059 glass (refractive index n ₁ = 1.53) is laminated as a first dielectric layer 31 on a substrate 33 on which an SiO ₂ film 41 of 1.44 is formed, and a second dielectric layer is formed thereon. 32
The optical waveguide 36 is formed by stacking SiO ₂ (refractive index n ₂ = 1.43). Then, on the surface of the optical waveguide 36,
Refractive index n _b of the dielectric plate 34 constituting the optical coupler by bonding with an adhesive 35 of 1.57. Here, the bonding portion 35
It is preferable that the refractive index difference between the
In order to suppress the reflectance at the boundary between the bonding portion 35 and the dielectric plate 34 to a certain value R or less, since the light is incident on the dielectric plate 34 almost perpendicularly, the bonding forming the bonding portion 35 is performed. Agent 1
The following relationship (9) between the refractive index n _p of the refractive index n _b and a dielectric plate 34 of 5 stipulated to stand.

(N _b −n _p ) ² / (n _b + n _p ) ² <R (9) For example, as the adhesive 35, a UV having a refractive index n _b of 1.57
Curable adhesive (trade name LX-2310 of Loctite)
When C) is used, since n _b is 1.57, the refractive index R is set to 0, so that the refractive index of the dielectric plate is n _p = 1.
It is preferable to use the dielectric plate 34 of 57.

In the optical coupler of the third embodiment, n _p =
When the dielectric plate 34 of 1.57 is used, the thickness s of the second dielectric layer 32 (SiO ₂ cladding layer) is set to 350 [n
m], and the thickness of the tapered portion 38 of the first dielectric layer 31 (# 7059 waveguide layer) changes from d = 320 [nm] to D = 570 [nm], and the taper length t Is 10
If the structure of [μm] (or 20 [μm], 30 [μm]) is used, the same radiation pattern as that of FIG. 5A can be obtained even with the optical coupler of FIG. The incident position characteristic (see FIG. 6A) having the same coupling efficiency as that described above is obtained.

In particular, similarly to the second embodiment, the taper length t is set to 1
When 0 [μm], the tolerance of the coupling efficiency to the incident position is expanded while suppressing the decrease in the coupling efficiency, and the tolerance to the incident position when the incident beam spot diameter L is 30 [μm]. (Defined by coupling efficiency of 60% or more) means that the first dielectric layer 31 (# 7059 waveguide layer) is not tapered to optimize the coupling efficiency (see FIG. 24). Is expanded from ± 7.5 [μm] to ± 9 [μm].

As shown in FIG. 12, in the optical coupler of the third embodiment, the dielectric plate 34 is connected to the optical coupler at the optimum incident angle θ _op.
Adjustment and arrangement so as to be perpendicular to the incident direction defined by the above (Formula (7)) (so that the angle φ formed by the dielectric plate 34 with respect to the optical waveguide surface is substantially the same as θ _op ). I do. After the position adjustment, the dielectric plate 34 is bonded to the optical waveguide 36 with an adhesive.
Fixed to

Further, an edge surface 37 is formed on the bonding portion 35 by the following method. Also in the third embodiment, the edge surface 3
7 establishes coupling to the optical waveguide 36, the adhesive 3
When an adhesive having a refractive index n _b of 1.57 is used for the sample No. 5, FIG.
The incident angle characteristics of the second optical coupler are the same as those in FIG. 7, and the optimal incident angle θ _i ′ to the surface of the optical waveguide is the same as that of the optical coupler structure 501 of the second embodiment. Accordingly, in the case of the third embodiment, the arrangement angle φ of the dielectric plate 34 is θ _op (= 68.2 °).
Is set equal to Thus, by setting the incident angle θ _i to the optical coupler to 68.2 °, the coupling characteristics of the optical coupler become the best. It is preferable that the surface of the dielectric 34 be coated with an anti-reflection coating in order to reduce reflection on the surface of the dielectric plate 34.

In another embodiment, n _p = 1.5
A is a dielectric plate 34 7,屈析ratio n _b in the adhesive 35
= 1.57 and the second dielectric layer 3
2 (SiO ₂ clad layer) is 350 [nm] in thickness, and the structure of the tapered portion 38 of the first dielectric layer 31 (# 7059 waveguide layer) is changed from d = 400 [nm]. D =
570 [nm], and the taper length t becomes 10 [μ].
m], the same expansion effect as the expansion effect of the coupling efficiency of the optical coupler structure 502 of the second embodiment with respect to the incident position is exhibited. Further, when the arrangement angle φ of the dielectric plate 34 is set to 69.1, the coupling characteristic of the optical coupler becomes the best by setting the incident angle θ _i to the optical coupler to 69.1 °.

For the above optical coupler structure, the optical waveguide 3
The height h of the edge surface 37 of the bonding portion from the surface of No. 6 may be determined so as to satisfy the condition of the above equation (8), as in the second embodiment.

<Manufacturing Process of Optical Coupler of Third Embodiment> Next, the manufacturing process of the optical coupler of the third embodiment will be described with reference to FIGS. explain.

First, as shown in FIG.
A photoresist 51 is applied on the optical waveguide 36 formed by laminating the first dielectric layer 31 and the second dielectric layer 32 on 3. Here, regarding the thickness of the photoresist 51,
The setting method of the second embodiment can be adopted so as to remove the influence of the recombination to a part of the bonding portion 35 protruding from the position of the edge surface 37 of the bonding portion 35 by the length P _L. That is, the height h of the edge surface 37 of the bonding portion 35 formed by the photoresist 51 may be determined so as to satisfy the condition of the above equation (8) in order to prevent a decrease in coupling efficiency due to recombination. The thickness w of the photoresist 51 is determined so as to satisfy the condition of w> h.

Next, as shown in FIGS. 13B and 13C, a groove 52 for injecting an adhesive is formed in the photoresist 51 by patterning. After the formation of the groove 52, the surface of the optical waveguide 36 is subjected to RIE to remove organic residues of the developing solution of the photoresist 61 and the altered layer formed on the surface of the optical waveguide.

Next, as shown in FIGS. 11D and 11E, the dielectric plate 34 is formed at an angle φ with respect to the optical waveguide 36 such that the incident surface is perpendicular to a desired incident angle. As described above, the position is adjusted using the position adjusting device 57 so that the edge B ′ is parallel to the edge C ′ of the groove 52 on the photoresist 51. After the adjustment, the dielectric plate 34 is placed on the surface of the photoresist 51 applied on the optical waveguide 36 while being held by the position adjusting device 57.

Next, in the state shown in FIGS. 11D and 11E, as shown in FIG. 11F, a photo-curable adhesive 35 is injected so as to cover the groove 52 for injection of the adhesive. . Subsequently, the bonding portion 35 is solidified by light irradiation, and the dielectric plate 34 is fixed. Here, the adhesive 35 used may be other than the photo-curable one. However, for the same reason as in the second embodiment, if a photo-curable adhesive such as a UV-curable one is used, the time required for fixing is short. In addition, there is an advantage that reduction in coupling efficiency due to displacement of the prism during fixing can be reduced.

Next, as shown in FIG.
After solidifying 5 and fixing dielectric plate 34, photoresist 51 is removed.

Here, the removal of the portion of the photoresist 51 sandwiched between the adhesive 35 and the optical waveguide 36 proceeds faster as the distance between the adhesive 35 and the optical waveguide 36 increases. In the third embodiment, too, the photoresist 51 having a high viscosity is used to apply a thick resist so that the portion of the photoresist 51 sandwiched between the optical waveguide 36 and the photoresist 51 can be easily removed.

More specifically, similarly to Embodiment 2 described above, a photoresist (trade name: positive type photoresist PMER) manufactured by Tokyo Ohkasha Co., Ltd. is applied in a layer of 15 μm, and the thickness w of the photoresist 51 is set to 30 μm in total. I have. Therefore,
The height h of the edge surface 37 of the bonding portion 35 is 30 μm.

Although FIG. 13 shows that the photoresist 51 is applied in a manner not to conform to the shape of the tapered portion 38 of the optical waveguide 36, the photoresist 51 is made sufficiently thick as described above. When applied, the thickness change of the tapered portion 38 is relatively smaller than the thickness of the photoresist 51, which means that the surface of the photoresist 51 after application is substantially parallel to the surface of the substrate 33. Is what you do.

<Ideal Structural Conditions in Optical Couplers of Each Embodiment> Next, ideal structural conditions in the optical couplers of the above embodiments will be described. As described above, when the beam spot diameter of the incident beam is around 30 [μm] and the effect of improving the tolerance on the incident position is ideal, the structure of the optical coupler is the taper length shown in FIG. This is a case where a radiation pattern when t is 10 [μm] is shown.
Therefore, the taper length t in FIG. 5A is 10 [μm].
The structure of the optical coupler with a small change from the radiation pattern of
This is a condition under which the coupling efficiency relating to the structure of the optical coupler can be kept relatively high.

Therefore, when the taper length t is 10 [μm], the refractive index n _b of the adhesive and the cladding layer (second dielectric layer)
N _c , the refractive index of the waveguide layer n _g , the refractive index of the substrate n _s ,
When examining the change of the radiation pattern when the thickness s of the cladding layer, the maximum thickness D of the waveguide layer, and the minimum thickness d of the waveguide layer are changed, FIGS. FIG.
(A), (b), FIG. 16 (a), (b), FIG. 17 (a)
It becomes like each figure up to. Incidentally, dashed line in the center in the figure _{n b = 1.57, n c =} 1.43, n g = 1.5
_{3, n s = 1.45, s} = 350 [nm], D = 570
[Nm] and d = 360 [nm].

FIG. 14A shows that the refractive index n _b of the adhesive is 1.
It shows the change of the radiation pattern when it changes to 56, 1.57, 1.58, there is almost no change in the radiation pattern, and the radiation increases as the refractive index n _b of the adhesive increases from 1.56 to 1.58. The pattern approaches a gentle slope.

[0129] FIG. 14 (b) shows the radiation characteristics when the refractive index n _c of the cladding layer changes with 1.42,1.43,1.44, the refractive index n _c of the cladding layer is 1. 42 →
As the value becomes 1.44, the radiation pattern approaches a curve having a gentle slope.

FIG. 15A shows that the refractive index _ng of the waveguide layer is 1.
It shows the change of the radiation characteristic when it changes to 52, 1.53, 1.55. The change in the radiation pattern when the refractive index _ng of the waveguide layer changes in this range is small, and _ns is 1.
As the distance becomes smaller from 55 to 1.52, the radiation pattern approaches a curve with a gentler slope.

FIG. 15B shows a change in the radiation pattern when the refractive index n _s of the dielectric layer portion of the substrate of the waveguide changes to 1.44, 1.45, and 1.46. Although no change in the radiation pattern so this time, the radiation pattern refractive index n _s increases the 1.44,1.45,1.46 inclination approaches gentle curve.

On the other hand, regarding the film thickness, the thickness s of the cladding layer is 300 [nm], 350 [nm], 400 [nm].
FIG. 16A shows the change of the radiation pattern when the change is made. As shown in this figure, the change in the radiation pattern is smaller than the change in the film thickness, and the smaller the thickness s, the closer the radiation pattern becomes to a curve with a gentle slope.

FIG. 16B shows that the maximum thickness D of the waveguide layer is 54.
The change of the radiation pattern when it changes to 0 [nm], 570 [nm], and 600 [nm] is shown. Maximum film thickness D is 60
When changing from 0 [nm] to 540 [nm], the radiation pattern approaches a curve with a gentle slope.

FIG. 17A shows that the minimum thickness of the waveguide layer is 320.
The change of the radiation pattern when it changes to [nm], 360 [nm], and 400 [nm] is shown. The change at this time is not so large, and the minimum film thickness is 320 [nm] →
When the wavelength changes to 400 [nm], the radiation pattern approaches a curve with a gentle slope.

From the above characteristic change, the taper length t is 10
[[Mu] m] When the above equation (1) condition the filled and substantially near optimal refractive index of the radiation pattern of the adhesive n _b, the refractive index n _c of the cladding layer, the refractive index n _g of the waveguide layer, The following ranges may be effective as condition ranges of the refractive index n _{s of the} substrate, the thickness _{s of} the cladding layer, the maximum thickness D of the waveguide layer, and the minimum thickness d of the waveguide layer.

[0136] _{1.56 <n b <1.58,1.42 <n} c <1.44, 1.52 <n g <1.55,1.44 <n s <1.46
_{, 300 [nm] <s <} 400 [nm], 540 [nm]
<D <600 [nm], 320 [nm] <d <400
[Nm] However, when all of these parameters are actually selected in combination so that the radiation pattern has a maximum point and has a variable pattern that gradually slopes from the position, the above-mentioned ( Even the condition of 1) is not satisfied. Therefore, an almost optimum range for the actual structure is a structure condition in which the refractive index _{ng of} the waveguide layer and the thickness s of the cladding layer are fixed. FIG. 18 shows the radiation pattern under the following conditions.

Condition 1: n _b = 1.58, n _c = 1.44,
_{n g = 1.53, n s =} 1.46s = 350 [nm], D
= 540 [nm], d = 400 [nm] Condition 2: n _b = 1.57, n _c = 1.43, n _g = 1.5
3, n _s = 1.45 _s = 350 [nm], D = 570
[Nm], d = 360 [ nm] Condition _{3: n b = 1.56, n} c = 1.42, n g = 1.5
_{3, n s = 1.44s = 350} [nm], D = 600
[Nm], d = 320 [nm] As shown in FIG. 18, when the radiation pattern is not largely deformed and the taper length t is 10 [μm], the range where the following condition A is satisfied is effective. This is one of the structural conditions of the coupler.

[0138] Condition _{A: 1.56 <n b <1.58,1.42} <n c <1.44,
_{n g = 1.53 1.44 <n s} <1.46 s = 350 [nm], 540 [nm] <D <600 [n
m], 320 [nm] <d <400 [nm] Similarly, when _ng = 1.52, _ng = 1.54, etc., the structural conditions are determined. For example, as shown in FIG. 19A, conditions: _ng = 1.52, s = 320 [nm] ( _nb =
_{1.58, n c = 1.44, n} s = 1.46, D = 540
[Nm], d = 400 [nm]), the condition: _ng
= 1.54, s = 380 [nm ] (n b = 1.58, n c
= 1.44, n _s = 1.46, D = 540 [nm], d
= 400 [nm]), the radiation pattern is almost the same as that of the condition 1 in FIG. 17 described above. When the taper length t is 10 [μm], the following conditions are also effective.

[0139] Conditions _{B: 1.56 <n b <1.58,1.42} <n c <1.44,
_{n g = 1.52 1.44 <n s} <1.46 s = 380 [nm], 540 [nm] <D <600 [n
m], 320 [nm] < d <400 [nm] Conditions _{C: 1.56 <n b <1.58,1.42} <n c <1.44,
_{n g = 1.54 1.44 <n s} <1.46 s = 320 [nm], 540 [nm] <D <600 [n
m], 320 [nm] <d <400 [nm] From the conditions A, B, and C, the following relational expression is approximately established between the thickness s of the cladding layer and the refractive index _{ng of the} waveguide layer.

S ≒ 3000 (1.53- _ng ) +350 [nm] Accordingly, when the taper length t is 10 [μm], the following structural conditions are preferable.

[0141] Conditions _{D: 1.56 <n b <1.58,1.42} <n c <1.44,
_{1.44 <n s <1.46 540 [} nm] <D <600 [nm], 320 [nm]
<D <400 [nm] 1.52 < _ng <1.54 where s ≒ 3000 (1.53- _ng ) +350 [n
m] Further, even when the taper length t is increased, the present invention can be applied to a case where the incident beam spot diameter is 30 μm, although the coupling efficiency is reduced. However, since the radiation pattern has a flatter shape, it is effective in that the coupling efficiency increases when the incident beam spot diameter is larger than 30 μm. Here, the taper length t is 15 as shown in FIG.
The change of the radiation pattern at [μm] is shown. N _g = 1.53 as shown in _{FIG, n b = 1.58, n c} = 1.4
4, n _s = 1.46, D = 540 [nm], d = 400
In the case of [nm], the radiation pattern at s = 400 [nm] shows a shape in which the radiation pattern under the condition A is entirely flattened. _{Further, n g = 1.52 (n b} = 1.5
_{8, n c = 1.44, n} s = 1.46, D = 540 [n
m], d = 400 [nm]), s = 430 [n]
m] gives a similar radiation pattern, _ng = 1.54
_{(N b = 1.58, n c} = 1.44, n s = 1.46, D
= 540 [nm], d = 400 [nm]), s =
A similar radiation pattern is obtained at 430 [nm]. From the above, the structural condition for improving the radiation pattern when the taper length t is 15 [μm] is the following condition E.

[0142] conditions _{E: 1.56 <n b <1.58,1.42} <n c <1.44,
_{1.44 <n s <1.46 540 [} nm] <D <600 [nm], 320 [nm]
<D <400 [nm] 1.52 < _ng <1.54 where s ≒ 3000 (1.53- _ng ) +400 [n
m] Conversely, even when the taper length t is reduced, the present invention can be applied to the case where the incident beam spot diameter is 30 μm although the coupling efficiency is reduced. However, since the radiation pattern becomes steeper, the incident beam spot diameter is 30 μm.
This is more effective in that the coupling efficiency increases when the value is smaller than m. FIG. 19C shows a change in the radiation pattern when the taper length t is 5 [μm]. As shown in the figure, _ng = 1.
53, n _b = 1.58, n _c = 1.44, n _s = 1.4
6, when D = 540 [nm] and d = 400 [nm],
The radiation pattern at s = 290 [nm] indicates a shape in which the radiation pattern under the condition A is sharpened as a whole. _{Further, n g = 1.52 (n b} = 1.58, n c = 1.4
4, n _s = 1.46, D = 540 [nm], d = 400
[Nm]) similar radiation pattern obtained with s = 320 [nm] when _{the, n g = 1.54 (n b} = 1.58, n c
= 1.44, n _s = 1.46, D = 540 [nm], d
= 400 [nm]), a similar radiation pattern is obtained at s = 260 [nm]. From the above, the structural conditions under which the radiation pattern becomes favorable when the taper length t is 5 [μm] are as in the condition F.

[0143] Conditions _{F: 1.56 <n b <1.58,1.42} <n c <1.44,
_{1.44 <n s <1.46 540 [} nm] <D <600 [nm], 320 [nm]
<D <400 [nm] 1.52 < _ng <1.54 where s ≒ 3000 (1.53- _ng ) +290 [n
m] Here, considering the taper length t [nm], s, _ng ,
s ≒ 3000 (1.53- _ng ) +
T, T ≒ 1000 (t−0.01) +350 [nm]. Finally, when these are put together, the structural condition of the optical coupler is condition G.

[0144] conditions _{G: 1.56 <n b <1.58,1.42} <n c <1.44,
_{1.44 <n s <1.46 540 [} nm] <D <600 [nm], 320 [nm]
<D <400 [nm] 1.52 < _ng <1.54 where s ≒ 3000 (1.53- _ng ) + T [nm], T ≒ 10000 (t−0.01) +350 [nm] ( 5 [μm] <t <15 [μm]) Note that the above conditions were obtained by simulation results by the present inventors.

<Range of tapered shape to which the present invention is applied>
Materials used for manufacturing an optical coupler such as the present invention include:
As the adhesive, those having a refractive index of 1.56 to 1.58 are frequently used due to the restriction of the refractive index and transmittance, and the material of the clad layer (second dielectric layer) is a refractive index such as SiO _2. Of 1.42 to 1.44 are frequently used. As a material of the waveguide layer (first dielectric layer), a refractive index of 1.52 to 1.5 such as # 7059 glass or SiON is used.
6 is frequently used, and such an element has a refractive index of 1.44, such as on a Si substrate (a surface on which a dielectric layer such as a SiO ₂ layer is formed) or a quartz glass substrate with low absorption.
Generally, materials of 1.45 to 1.45 are used as substrates.

Therefore, when the tapered shape is examined under such conditions, FIG. 14 (a), (b), FIG. 15 (a), and FIG.
(B), FIGS. 16 (a), (b), FIGS. 17 (a), (b)
In the state shown in FIG. 5, a radiation characteristic close to the radiation characteristic showing the high coupling efficiency shown in FIG. 5 is obtained. Here, since the material of the optical coupler as in the present invention is almost determined, it can be said that the condition of the taper shape obtained from these figures is an ideal condition.

That is, the condition of the taper shape is as follows.

5 [μm] <t <15 [μm], 300
[Nm] <s <400 [nm], 540 [nm] <D <
600 [nm], 320 [nm] <d <400 [nm]

[0149]

According to the optical coupler of the present invention described above, the radiation pattern of the optical coupler is a deformed radiation pattern that is substantially uniform in the traveling direction of light in the optical waveguide. It is possible to increase the tolerance of the coupling efficiency to the incident position.

In addition, since the line of intersection with the surface of the optical waveguide is formed as a straight line at the bonding portion, and an edge surface having a portion not in contact with any of the light introducing means and the surface of the optical waveguide is formed.
The distance between the edge of the tapered portion of the dielectric layer and the line of intersection between the edge surface of the bonding portion and the optical waveguide surface can be accurately determined. Therefore, the deviation of the distance between the edge of the tapered portion of the first dielectric layer and the edge surface of the bonding portion from the optimum value can be easily eliminated, and a decrease in the coupling efficiency can be suppressed to a minimum.

Further, according to the optical coupler of the second aspect, it is possible to set a suitable tapered shape range when using a material frequently used in this type of optical coupler.

In the optical coupler according to the fourth aspect, the height h of the edge surface of the bonding portion from the surface of the optical waveguide is set as follows:
When setting is made so as to satisfy the above expression (2), the possibility that the bonding portion functions as a thin film due to the multiple reflection light generated by the reflection at the interface between the adhesive and the bottom surface of the prism and the coupling efficiency becomes unstable is completely eliminated. Can be removed.

According to the optical coupler of the fifth aspect, the dielectric plate is easier to manufacture than the prism, so that there is an advantage that the manufacturing cost can be reduced.

In addition, according to the optical coupler of the sixth aspect, since the configuration in which the antireflection coating is applied to the dielectric surface is adopted, there is an advantage that the reflected light can be reduced.

According to the manufacturing method of the present invention, the position of the line of intersection of the edge of the adhesive with the surface of the optical waveguide is adjusted with respect to the edge of the tapered portion of the first dielectric layer by photolithography. Therefore, the distance between the line of intersection of the edge of the bonding portion with the optical waveguide surface and the edge of the tapered portion of the first dielectric layer can be determined with high accuracy. In addition, since the linearity of the line of intersection between the edge surface of the bonding portion and the surface of the optical waveguide can be realized by the photomask, highly accurate linearity can be realized.

According to the method for manufacturing an optical coupler of the present invention, the prism is arranged on the photoresist so as to bridge the groove formed by the photoresist. Since it is in contact with the surface at two places, the parallelism between the optical waveguide surface and the prism bottom surface can be improved. As a result, the base angle φ of the prism determined so that reflection at the incidence surface is minimized when the light is incident at the optimum incidence angle.
And the angle between the incident angle to the optical waveguide surface and the angle formed by the incident angle can be reduced. For this reason, it is possible to suppress a decrease in coupling efficiency due to a shift of the incident angle to the optical coupler from the optimum incident angle.

In addition, according to the method for manufacturing an optical coupler of the ninth aspect, the thickness w of the photoresist and the height h of the edge surface of the bonding portion from the surface of the optical waveguide are w> h. , It is possible to prevent the bonding portion from functioning as a thin film.

Further, according to the method for manufacturing an optical coupler according to the tenth aspect, an RIE process is employed as a post-process of forming a groove on the photoresist. The organic residue and the altered layer formed on the optical waveguide surface can be removed, and the adhesive strength to the optical waveguide can be increased.

Further, according to the method for manufacturing an optical coupler of the present invention, it is possible to shorten the curing time and minimize the change of the adjustment position in the curing process by using the photocurable adhesive as the adhesive. Can be

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an optical coupler according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing r _n in equation (1).

FIG. 3A is a graph showing a coupling efficiency incident position characteristic in which the vertical axis represents the coupling efficiency and the horizontal axis represents the incident position, and the distance between the edge of the tapered portion and the edge of the bonding portion is used as a parameter; FIG. 2B is a cross-sectional view illustrating a test optical coupler that has obtained the experimental result of FIG.

FIG. 4 is a sectional view of an optical coupler according to a second embodiment of the present invention.

5A and 5B are graphs showing the radiation characteristics of the optical coupler, with the vertical axis representing the normalized radiation intensity and the horizontal axis representing the distance from the edge of the bonding portion.

6A and 6B are graphs showing the coupling position dependence of the coupling efficiency, with the vertical axis representing the coupling efficiency and the horizontal axis representing the incident position.

FIG. 7 is a graph showing an incident angle characteristic of the coupling efficiency with the vertical axis representing the coupling efficiency and the horizontal axis representing the incident angle.

FIG. 8 is a sectional view showing another example of the optical coupler to which the present invention is applied.

FIG. 9 is a sectional view showing how to determine the height h of the edge surface of the bonding portion.

FIG. 10 is a process chart showing a manufacturing process of the optical coupler of the second embodiment.

FIG. 11 is a sectional view showing another example of the optical coupler to which the present invention is applied.

FIG. 12 is a cross-sectional view of an optical coupler according to a third embodiment of the present invention.

FIG. 13 is a process chart showing a manufacturing process of the optical coupler of the third embodiment.

14A is a graph showing a change in a radiation pattern when the refractive index of the adhesive is changed, and FIG. 14B is a graph showing a change in the radiation pattern when the refractive index of the second dielectric layer is changed. The graph shown.

15A is a graph showing a change in a radiation pattern when the refractive index of the first dielectric layer is changed, and FIG. 15B is a graph showing a change in the radiation pattern when the refractive index of the substrate is changed. Graph.

16A is a graph showing a change in the radiation pattern when the thickness s of the second dielectric layer is changed, and FIG.
9 is a graph showing a change in a radiation pattern when the maximum thickness of a dielectric layer is changed.

17A is a graph showing a change in the radiation pattern when the minimum thickness of the first dielectric layer is changed, and FIG. 17B is a graph showing a change in the radiation pattern when the taper length is changed.

FIG. 18 is a graph showing a comparison of radiation patterns under conditions 1, 2, and 3.

19 (a) to 19 (c) are graphs each showing a radiation pattern.

FIG. 20 is a sectional view showing a conventional example of an optical coupler.

FIG. 21 is a sectional view showing another conventional example of the optical coupler.

FIG. 22 is a sectional view showing another conventional example of the optical coupler.

FIG. 23 is a graph showing types of radiation patterns.

24 (a) is a cross-sectional view showing a conventional optical coupler for a test obtained from the experimental result of (b), FIG. 24 (b) is the coupling efficiency on the vertical axis, and FIG.
7 is a graph showing the incident position characteristics of the coupling efficiency of the conventional example, with the incident position shown on the horizontal axis.

[Explanation of symbols]

1, 11, 31 First dielectric layer 2, 12, 32 Second dielectric layer 3, 13, 33 Substrate 4, 14 Prism 5, 15, 35 Adhesion 6, 16, 36 Optical waveguide 7, 17, 37 Adhesion Edge 18, 38 Taper 19, 39 Edge of taper 20 Reflection / incidence prism 21, 40 Si substrate 22, 41 SiO ₂ layer 34 Dielectric plate 51 Photoresist 52 Adhesive injection groove 53 Position adjusting device

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Naoto Uezuka 5-1-1, Hidaka-cho, Hitachi City, Ibaraki Prefecture Within the Opto-System Laboratory, Hitachi Cable, Ltd. (72) Inventor Hirofumi Ouchi Date, Hitachi City, Ibaraki Prefecture 5-1-1 Takamachi Hitachi Cable, Ltd. Optro System Laboratory

Claims (11)

[Claims] A first dielectric layer laminated on the substrate, the first dielectric layer having a portion in which a film thickness changes in a tapered shape in an X-axis direction in which incident light travels after coupling, and a first dielectric layer of the first dielectric layer; An optical waveguide composed of a second dielectric layer laminated thereon,
An optical coupler for causing light to enter the surface of the optical waveguide at a predetermined angle by light introducing means bonded to the optical waveguide via a bonding portion, wherein the bonding portion has an intersection with the surface of the optical waveguide. The line becomes a straight line,
An edge surface having a portion not in contact with either the light introducing means or the surface of the optical waveguide; and a section X _{n-1 having} a portion where the film thickness of the first dielectric layer changes to a tapered shape. <X <and the radiation coefficient alpha _rn in X _n, when the distance from the edge surface of the adhesive portion is the amplitude at the position of X _n and a _n, light of wavelength λ by using the optical coupler the so that radiation pattern when radiated from the optical waveguide, satisfies the following conditions _{(1), a n-1 (1-} r n) <a n (1-r n + 1) ... (1 ) _{where, r n = exp (k 0} α rn △ X) k 0 = 2π / λ △ X = X n -X n-1 first dielectric layer optical coupler set a tapered shape. 2. The taper length t of the taper shape, the thickness s of the second dielectric layer, and the maximum thickness D and the minimum thickness d of the first dielectric layer satisfy the following conditions. [Μm] <t <15 [μm], 300 [nm] <s <
400 [nm], 540 [nm] <D <600 [n
m], 320 [nm] <d <400 [nm] The optical coupler according to claim 1, wherein the tapered shape is set. 3. The height h of the edge surface of the bonding portion from the surface of the optical waveguide is represented by r _A of the Airy radius of the incident beam spot, and θ ₁ ′ of the incident angle on the surface of the optical waveguide. 3. The optical coupler according to claim 1, wherein h> 2r _A / sin θ ₁ ′ (2) is set so as to satisfy the condition of the following expression (2). 4. The optical coupler according to claim 1, wherein said light introducing means is a prism. 5. The optical coupler according to claim 1, wherein said light introducing means is a dielectric plate. 6. The optical coupler according to claim 5, wherein an antireflection coating is applied to a surface of said dielectric plate. 7. The method for manufacturing an optical coupler according to claim 1, wherein a step of applying a photoresist to a surface of the optical waveguide, and an step of injecting an adhesive onto the photoresist. Forming a groove for the optical waveguide, adjusting the position of the light introducing means on the surface of the optical waveguide, and arranging the light introducing means on the surface of the optical waveguide, and fixing the photoresist. And a method for manufacturing an optical coupler. 8. A method for manufacturing an optical coupler, wherein the light introducing means is a prism, wherein a step of applying a photoresist to the surface of the optical waveguide, and forming a groove for injecting an adhesive on the photoresist. A step of adjusting the position of the prism on the surface of the optical waveguide so as to straddle the groove; a step of bonding and adhering the light introducing means to the surface of the optical waveguide; And a method for manufacturing an optical coupler. 9. The thickness of the photoresist w satisfies the following condition: w> h, where h: the height of the edge surface of the bonding portion from the surface of the optical waveguide is set. A method for manufacturing the optical coupler according to claim 8. 10. The optical coupler according to claim 7, further comprising a step of performing an RIE process on a surface of the optical waveguide as a post-process of forming a groove on the photoresist. Manufacturing method. 11. The optical coupler according to claim 7, wherein the step of bonding and fixing the light introducing means to the surface of the optical waveguide is performed using a photo-curable adhesive. Manufacturing method.